Secrets of the ultimate trophy fish: the physiological ecology and behaviour of white sturgeon (Acipenser transmontanus Richardson, 1836) after angling

Abstract

Around the world, human activities and climate change are altering ecosystems at unprecedented rates, which in many cases is outpacing our capacity to understand and predict the potential impacts on biodiversity. Fishing is one of the most pervasive anthropogenic stressors to fish populations worldwide, and so examination of fishing stressors is needed, especially in a changing climate. This thesis aimed to understand the physiological and behavioural consequences of catch-and-release (C&R) angling to white sturgeon, Acipenser transmontanus, in the lower Fraser River (LFR), British Columbia, Canada, with consideration of capture under different, seasonal river temperatures. White sturgeon are prized as a trophy species, with the largest individual sturgeon measuring more than 3 metres in length and putting up angling fight times of more than an hour. Currently, white sturgeon in the LFR are considered Threatened by the Committee on the Status of Endangered Wildlife in Canada. Despite conservation concerns, there are few regulations for the C&R fishery. Given the lack of restrictions, and knowledge that the Fraser River is warming due to climate change, I assessed the short- and long-term effects of C&R angling on white sturgeon in the LFR using physiological sampling of stress metabolites, a refined reflex impairment index, and acoustic telemetry. After angling wild sturgeon on the river, lactate concentrations were consistently higher in fish enduring long fight times, indicating anaerobic exhaustion. Here and in complimentary lab studies with captive sturgeon, reflex indicators of impairment were predicted by angling fight times and plasma lactate levels, and this effect was exacerbated in summer when temperatures are higher. Ultimately, recovery time from physical exhaustion increased with the duration of angling stress. Using tri-axial accelerometer acoustic transmitters, a snap-shot into the immediate post-release recovery behaviour of wild sturgeon revealed high inter-individual variability. Sturgeon required a recovery period after angling, which occurred consistently in nearshore environments. Long-term monitoring revealed high post-release survival (100%), indicating some resilience of sturgeon to angling, but there was some evidence of transient sublethal effects, and the fitness implications are still unknown. This is the most comprehensive examination of the impacts of recreational angling on a wild population of sturgeon. The results from this research revealed intriguing variance in the physiological and behavioural response of individual white sturgeon to C&R recreational angling, with some degree of environmental temperature dependence, and highlights the importance of understanding the drivers of such variation when managing fisheries.